Compass



sept. 15, 1936. R, GUNN 2,054,318

' COMPASS A Filed May l2, l932 4 Sheets-Sheet l /OSS Gun/y dwf/w s.

R. .GUNN

Sept. 15, 1936.

COMPASS Filed May 12, 1932 4 Sheets-Sheet 2 gwwmtoz R. G UNN COMPASSSept. 15, 1936.

Filed May l2, 1952 4 Sheets-Sheet 5 Sp E5, i R GUNN 2,054,318

COMPASS Filed May l2, 1932 -4 Sheets-Sheet 4 @Minimum SWW/nto@ Patented.Sept. 15, 1936 UNITED sTATEs PATENT o-FFICE" (Granted under the act ofMarch s, 1883, as amended April 3o, 192s; 37o o. G. '157) This inventionrelates to compasses, and has for an object to provide means forcancelling out spurious deviations of a magnetic compass due to the rollor pitch of the craft on which the compass is used and thus make thecompass more reliable and accurate.

A particular object of the invention is to provide a compensatingmagneticdevice capable of producing a magnetic field adjacent theresponsive means of a magnetic compass mounted to turn or rotate about afixed axis, that is, a compass rigidly mounted on the craft carrying it,and gravitationally orienting said compensating device independently ofthe responsive means of the compass so that' it willautomaticallycompensate for the vertical component of the earths magnetic eld orextraneous magnetic fields regardless of tipping and rocking of thecraft on which the compass is mounted.

It is also an object of the invention to provide means for reducing thevertical component of the earths magnetic eld in the compass to smallvalues, or to provide means for compensating for the, extraneous E. M.F. -or magnetic forces pro;

2 duced by the vertical magnetic eld, so that this vertical component orfield Will have practically no effect on the indication.

'Another object of the invention is to 'provide easily adjustable meansin a compass to compensate for the permanent magnetism Which'an ironcraft inevitably possesses, thus rendering the compass more accurate andreliable.

A further object is to provide an induction compass in which it ispossible to rigidly mount all rotating parts on the craft itself, andexible higdspeed universal driving means are elimina Another object ofthe invention is to provide,

arrugged inductor compass in which the flexible shaft heretofore usedtoset the course may be entirely eliminated and the desired courseselected by purely electrical means.

In short it is an important purpose of this invention to provide asimplified, more rugged and reliable inductor compass suitable for useon mobile craft, and to achieve reliability and yet retain the lightestconstruction possible.

Other objects and advantages will become apparent from the followingdescription taken in connection`v with the accompanying drawings whereinseveral embodiments of the invention are shown. However, it will beunderstood thatthe invention is not .limited to the details disclosed,

but includes all such variations and modifications as fall within thespirit of the invention and the scope of the appended claims.

In these drawings:

Fig. 1 is a vertical section of an inductor compass rigidly, mounted onthe frame of an air- 5 craft, showing one form of my improved com-lpensating devices applied thereto;

Fig. 2 is a. schematic diagram of thedevlce of Fig. 1 showing theelectrical connections;

Fig. 2a. is a diagrammatic view illustrating the 10 effect of thecompensator;

Fig. 3 is a transverse section of the propelling means which may be usedfor rotating the lnductor of the device of Fig. 1;

Fig. 4 is a detail of a portion of the orientlng l5 device;

Fig. 5 is a plan view of a. compensating device which may be used eitherwith an inductor compass or may also be used with various other typesofCompasses to compensate for various 20 extraneous magnetic ields, suchfor example as a permanent magnetism, which an iron craft inevitablypossesses;

Fig. 6 is a. similar view of a modified construction to be used for thesame purpose as the 25 Ydevice of Fig. 5;

Fig. 7 is a partial side elevation and a partial section of a. portionof an inductor compass, showing a modied form of compensator;

Fig. 8 is an enlarged view of the compensator 30 and the mountingtherefor used in Fig. 1, the compensator being shown in elevation andthe compass in vertical section;

Fig. 9 is a top plan view thereof;

Fig. 10 is a side elevation .of the upper end 35 of a compensatingmagnet showing its shape for a. certain purpose;

Fig. 11 is a top plan view thereof;

Fig. 12 is a. side elevation from thev right of Fig. 10;

, Fig. 13- shows aside elevation of a modified form of the compensatorwith its mounting in vertical section;

- Fig. v14 is a partial vertical section and partial side elevation oflan inductor system showing 46 still another/form of compensatingdevice;

Fig. 15 is a partial side elevation and a partial vertical section witha diierent arrangement of inductor system involving a rugged inductorcompass in which the flexible shaft heretofore used 50 to set the courseis entirely eliminated, and the desired course is selected by purelyelectrical means;

Fig. 16 ia a .wiring diagram for the device of v Fig. 15; Ii

5 showing my improved compensating device ap- Fig. 19 is a transversesection substantially on the line 'IQ- I8 of Fig. 18.

All magnetic compasses indicate primarily direction parallel to thesurface of the earth, and

hence employ for their action the horizontal component of the earthsmagnetic field. The vertical component of the earths magnetic eld, whichhas a finite value inall regions except at the magnetic equator,tcontributes nothing to the action of the compass as a directionindicator. However, when the vertical component of the earths magneticheld is present deviations ofthe compass needle (when magnetic 2.0needle is employed) or plane oi.' the inductor of an inductor compassfrom the horizontal introduces troublesome forces and incorrectindications. If not corrected for these would occur especially when anairship rolls or pitches or 25 when it is inclined from the horizontalin flight.

To overcome these diiliculties I have provided improved means either forreducing the vertical component of the earths magneticv eld in thecompass to small values or to zero so that 30 it will have practicallyno eilect on the indication of the compass, or I have provided means forcompensating for the extraneous E. M. F. or magnetic forces produced bythe vertical magnetic field so that it does not affect the indication y35 of direction.

It has been known to reduce the effect of the vertical componentby'mounting the .compass or the inductor on gravitationally orientingsupports so that as the ship pitches yand rolls the inductor for exampleis always maintained in vsubstantially the horizontal plane, but thishas V-numerous vdisadvantages especially involving complicated and heavymechanism for mounting the moving elements, and particularly as involv-45 ing the use of a. flexible high speed driving shaft.

With my present system these jobjections are overcome as-the compass andthe rotating elements may be rigidly mounted on'the frame of the craft,thus doing away with complicated 50 mounting constructions and alsoeliminating the use of high speed exible driving shafts and associateddevices.

Referring rst to Figures 1 to 4 inclusive, there is shown in thesefigures a simplied, more rug- 55 ged, and reliable inductor compasssuitable for `use on mobile craft, particularly aircraft.

is so constructed as to achieve reliability and yet retain lightestconstruction possible. 'Ihe inductor compass illustrated in certainrespects is similar to that disclosed in my prior application. SerialNumber 406,702, for Inductor compass,

filed November 12, 1929, particularly in that it employs a breakermechanism in place of a commutator for rectifying the current generatedin '.65 order to secure stability and reliability in operation, thisbreaker rectifier being substantially the same as the synchronouscontact mechanism disclosed in the said prior application.

This improved device comprises a support 2l 70 "and housing 2| rigidlymounted on the frame of the air craft indicated at 22. Although it isrigidly mounted on the frame it `is so mountedA as to be tumable about averticalaxis for orient- -ing the inductor system for the desiredcourse.

175 Mounted lin this frame and housing is a vertical shaft 23 driven by.any suitable means, but in the present instance by a propeller or fan24. which is mounted in the slip stream of the air craft propeller anddesigned to run at substantially constant speed. This propeller is shownmore in detail in Fig. 3 in which is shown curved blades 25 secured atone end as shown at 2i,

to the supporting structure. The blades are made of some spring orflexible resilient material and are bent to a curved shape approximatelyas shown in the drawings. The inner ends of' the blades are free andmayor may not carry weights 2l. It will be evident that centrifugalforce may throw the weights 21 outwardly more lor less depending on the-speed of the fan. 1As

the blades are straightened the driving force of the air on the bladesis reduced, therefore by cally varies with the speed of the slip stream,and` to maintain the rotating speed substantially con stant, as theblades form more eiiicient driving means when they are in the innerposition shown A infulllinesinFlgurelthanwhenintheouter position asshown in the dotted lines, and therefore automatically compensate forvariations in the driving force.

Mounted on the shaft 23 is the inductor 2l of any suitable type, andwhich may consist of a v soft iron or permalloy core 2l wound withsuitable conductors in such a way that the rota.- tion of the assemblyI6` induces an E. M. F. in the windings of the coils due to cutting ofthe coils across the earth's magnetic field. The

E. M. F. or current generated is conducted to the breaker mechanismindicated ai:V ll by the contactsI2and3IimiicatedinFlgure2,thesecontacts being of course insulated, as for example by.mounting oninsulating supports u and 35. Fromthebreakerorrectierm Il the rectifiedcurrent is conducted tothe indicator meter 38. 'I'he angular position ofthe generator structure with relation to some fixed point on the craftmay be indicated by a counter Il which is ordinarily geared to thegenerator` in suchk a ratio' that 360 divisions of the countercorresponds to one complete revolution. 'lhat is tosaythereadingcanbeadjustedtogivethemagnetic azimuth of some selectedline on the craft. To accomplish this result the upright extension Ilrofthe housing and support 2l is mounted toturninthebearingllontheframesoasto turn about the axis of the verticalshaft 23. Any suitable gearing-such as a -worm gear on the extension Il,and'a worm Il driven by flexible shaft operated by any suitable means,such as va crank located where itiseasilyaccessible by the pilot.Counter 3l may be geared to this crank and shaft by the worm and gear"-45 toindicate the position of the inductor system' Vairis so that theindicator Il indicates zero when the craftis on course, and then thepointer will move to the right or left if the craft moves o! .A courseto right or left to change the relative posltion of the inductor to theearth's magnetic field. u

is off course and how much.

The breaker'or rectifier is indicated diagrammatically in Figure 2 ascomprising a rocking arm Ila pivoted at Sib and carrying contacts 3ioand Sid connected to the brushes or contacts 32 and 33. The arm has afork Sie operated by a cam or eccentric on the shaft 23 to move thecontacts llc yand Sl back and forth between the stationarycontacts lig',llh, 3H, and 3U in synchronl sm with the rotation of the inductor coils30 and thus rectify the current generated in these coils and supply therectied current to the indicator 36. The rectifier is mounted on aninsulating 'support Slk which may be oriented by any suitable means, notshown, to adjust it to the proper relation to the inductor.

In general, as the craft dips either fore or aft or laterally extraneousE. M. F.s will be induced in the-inductor system 28 by the verticalcomponent of the earth's magnetic field. As indicated above a universalmounting has been used to keep the inductor assembly I6 in a horizontalplane so that the effect of the vertical component ci the earth'sv fieldfor any given latitude is substantially constant. but this involves acomplicated mounting structure and also requires a universal or flexiblehigh speed drive which mechanically is highly undesirable. I haveovercome this difficulty with a simple compensating mechanism whichconsists of a magnetic means which is so mounted as to either compensatefor the undesirable effects of the vertical component of the earth'smagnetic field either by reducing or cancelling out this component or bycompensating for the extraneous E. M. F. or magnetic forces produced bythis vertical magnetic field.

Various devices may be used for accomplishing this result.` In Fig. 1the device illustrated for doing this comprises a permanent magnet 46.mounted on a gimbalor universal support, that shown comprising ahorizontal pivot 41 for mounting the magnet in a ring 48 which is inturn supported by horizontal pivots 49 at right angles to the pivots 41,and therefore the magnet may swing or tip in all directions. The lowerend is weighted as indicated at 50 so as to automatically maintain theunit 46 in-the upright or vertical position in all positions of theaircraft. The pivots 'I9 are mounted on a ring support 5I inthe cylinder52 and the walls of this support have elongated slots 53 through whichextend mount- -ing bolts 54. It will be evident that by loosening 'thesebolts the support stand the magnet as may l'be adjusted up and down, orthat is toward and from the inductor 28 to vary the effect of themagnetic field of the compensator on the inductor. It is also desirablethat the magnet in the normal position be in alignment with the axis ofthe shaft 23. and therefore the mounting 52' y is supported so that itmay be adjusted to bring the magnet into this position. Therefore themounting bolts 55 may pass throughv enlarged 'openings or vslots 5i inthe bottom wall of the housing 2| to permit this adjustment.v

With this arrangement the magnet t6 introduces into the compass amagnetic field which ,changes its magnitude and direction with chang-'ing attitude of the craft in such a manner that .755e horisdntalplaneeffect of vertical '3 earths'magnetic eld or the vertical component ofthe earth's magnetic field represented by the lines 51 is compensatedfor by a counter E. M. F..

due to the fleld provided by the magnet 46, and

will be evident that the magnet can beadjuste'd to cancel out the E. M.F. due to the vertical component .of the earth's eld, the adjustmentdepending' on the strength of the field. If now the,

the line fc then the magnet 46 is shifted to thei position h. and theflux i due to the vertic'all component `of the earth's magnetic fieldwill be' compensated for by the counter fiux i created by the magnet 46.As the angular relation of the field or flux created by the magnet withrespect to the rotating inductor varies with the attitude of the ship,because the magnet always remains' vertical due to its beinggravitationally oriented and maintains this position due to theuniversal mounting andthe weight 50, it will be evident that themagnitude and direction of this flux changes with the attitude of thecraft in such a manner that the compensating E. M. F. or compensatingdue to the adjustable mounting of uns magnet it v5 magnetic force willjust cancel the effects of the unwanted vertical magnetic field.

To prevent rapid oscillation of the magnet due to pitching and rollingof the ship the oscillations may be damped by producing' friction on itsmounting pivots, such as by friction washers, or

the container 52 may be closed and hold a suitable damping liquid.

Further, under certain conditions it may happen-- that the fore and aftmagnetism of a craft :is quite different in its distribution to thelateral magnetism. Good compensation may be attained under this specialcondition by a single magnet if the magnet pole tip is made asymmetricalin a..

suitable manner to differentiate the two magnetic distributions. Such atip is shown in Figs. 10, 1l and 12. The tip 59 is asymmetrical beingstraight in -one direction and tapered at its opposite lsides in a'planeat right angles thereto.:

' Moreover, since the earth's vertical magnetic field changes withmagnetic latitude the strength of the magnet I6 or its position withrespect to the inductor generator or the compassne'edle system shouldchange with the magnetic latitude. This can be readily accomplishedeither by making the magnet asmall electro magnet as indicated in Fig.13 and varying the current through the coil =64 or'by shifting themagnet with respect to the inductor generator, the'magnetic needle, orboth.v

In Figs. 1, 8 and 9 the adjustment of the compensating effect is securedby adjusting the mounting 5l toward and from the inductor or needle asdescribed above. In Fig. 13 the compensating magnet comprises a softiron or perrn-.

alloy core mounted for universal rocking move- 'ment on the gimbalsystem 6|, this comprising a ball and socket 62 in which the ball 83 onthe core may turn in all directions. As the lower partjof "the coreis/heavier than -the upper part it will be automatically retained in theupright position. .This core is surrounded by Ithe exciting coil Il'supplied with current from any suitable battery Si, and this currentmay be adjusted by an adjustable resistance to vary the strength of thecom-75 4 pensating field. This masnetfwith its coil may be mounted onthesupport .or sleeve I1 in a container or mounting l2 and beadjustedthereln toward or from the magnetic needle or inductorvsystemofthiecompass,thesameasin'thearnngemencinm. 1.aamiathusgivmganadditional adjustment for its compensating effect.Thismaybeaccomplishedbythebolts Il passing through the elongated slotsil.

Besides the method of introducing a magnetic field which changesits'magnitude and direction with changing attitude of the craft in sucha shaft to turn therewith. This arrangement is rlsldly mounted on theframe of the craft properihdicated at 1l. As indicated above, in thepast it has been the practice to mount such an inductor generator on auniversal mounting so that its' axis of rotation and the shaft 1I isalways maintained in the vertical position. 'I'his required a hih speed,universal or flexible drive shaft which for mechanical reasons is veryundesirable. With this present arrangement however, this flexible driveshaft is entirely eliminated and the device is rigidly mounted'by asimple construction on the frame of the craft. In order however, tocom'- pensate for the pitch and roll of the shipthe vertical componentofthe earth's magnetic fleld is reduced to zero in the rotating inductorsystem by the gravitational oriented electro magnet 14. For this purposea suitable direct current is led from any suitable source, such as abattery 'I5 to circulate through the winding of the coil I6 in an ap-:proprlate direction to produce a magnetic field in the region of theinductor generator ss which just cancels the vertical component of-theearths' magnetic field in this inductor.

the eld may be varied by the adjustable resistance 11. 'I'his electromagnetis mounted on a universal mounting comprising a socket 1l. and aball 1U so that it mayV rock in all directions andA therefore it ismounted in such a manner that the axis of the solenoid is alwaysvertical irrespective .of the position of the craft, or that is, theshaft Il and its mounting 1n. v'I'hus in any given magnetic latitudedeviationsv in thev indicationsof 'the compass which would otherwisearise from the pitch and roll of the ship are non-existant in thisdevice since-there isno vertical magnetic eld in the inductor system.The tipping of the ship will slightly reduce the induced E. M. F.produced by the Inductor generator l2, but will not shift the positionor direction of indication of the true course. A large permanentmagnetor a system of permanent magnets gravitationally oriented willaccomplish the same result, but

they must be so mounted that the strength of their fields could beadjusted.

A particular advantage of this device using the types of compensatorabove described lies in the factthat by their use it is possible torigidly mount all rotating parts on the craft itself 'a 1d flexible highspeed universal drives are eliminated. It is also to be noted that thegravitationally oriented system, that is the compensator, is at rest.and therefore there no gyroscopic forces The strength of to throw it outof adjustment or to affect its accuracy. For .this reason it is moreeasily damped and the compass comes to its true indication with vgreaterrapidity than has'been possible withany of the earlier designs.

'Ihe principle of my invention may 'also be used to compensate for thepermanent magnetism which an iron craft inevitably possesses, and

which affects the indication of the compass carried by the craft. InFigs. 5 and 6 are shown constructions which may be used for thispurpose. They may be used with any magnetic compass, either a needlemagnet or an inductor. In

Fig. 5 the dot and dash lines II represent a rotating lnductcr which maycorrespond with the inductor 28 of Fig. 1. Located adjacent the plane ofrotation of the inductor are two arms Il and 82' of -any suitablemagnetic material such as soft iron, permalloy, or any' other magneticmaterial of low cohesive force. These arms are mounted on a mountingslab U3 of any suitable material, such as bakelite or brass. These armsoperate as collectors of magnetic flux. Mounted adjacent thesecollectors 8| and l2 are two permanent magnets 84 and 85 secured on anon-magnetic mounting I6. It will be noted that the magnets 84 and 85are mounted on opposite sides of the collectors Il and l2, but that theyare adjustable toward and from these collectors. In the present instancethe member I6 has elongated slots 81 through which are headed studs 8lmounting the member l0 on the block Il. The member 86 has al flange 89through which ispivoted an adjusting screw t! threaded in a lug ilcarried' by the block It will thus be evident that by turning the screwIl the block 8B may be adjusted laterally with respect to the members 8|and B2 and` thus the magnets Il and Il may be adjusted vtoward and fromthe members Il and 82. Thus if the magnet I4 is mounted with its northpole to the left and its south pole to the right as indicated by theletters N. and S. and the,

magnet I! is arranged with its north pole to the right and its southpole to the left, then the members Il and l! will be polarized tocorrespond with the magnet located closest to it. If the two magnets'are located equidistant from the members Il and l! then they neutralieeach other and the members Il and l2 are not polarized, but if the screw$0 is adjusted to bring the magnet Il closer to these elements then theelement li would be of south polarity. while the element 82 would be ofnorth polarity. If the magnets are adjusted in the opposite direction tobring the magnet II closer to the elements .Ii-02 then Il would be ofnorth polarity, while I2 would be of south polari'- ty. It will also beevident that the'magnltude kof the flux in these elements lI-II woulddepend on the degree of proximity of the magnets to these elements, andthe closer either magnet is to these elements the greater the ilux.Therefore it will be evident that the compensator, involving theelements 8I82 and the magnets is capable of producing a magnetic fieldfrom some finite value in one direction to the same value in the oppo-`site direction continuously by means of a simple adjustment. It willalso be evident that the volume of the region compensated is comparableto the volume ofthefixiductor or the magnetic needle system of'the-compass. Thus by turning the screw 9|! a magnetic field may beproduced at some outside point of any reasonable magnitudeand direction.Therefore iif the line $2 represents the permanent magnetism which theiron craft on which the compass is mounted possesses,

then by adjusting the magnet 94 toward the elements 9|-92 to the properposition a eld will be created by these elements of suitable magnitudeand direction to compensate for the iield 92. In a. practicalarrangement two or more systems similar to Fig. would be employed andthese' would be arranged at right anglesto each other.

In Fig. 6 is a slightly'diierent arrangement for securing the sameeiIect. Here the collector elements 93-94 correspond to theelements 9|82of Fig. 5 mounted adjacent the rotating inductor 99. The magnets 99and-99 are mounted on a pivot 91 and cross each other and one of themrests against the end o! an adjusting screw 99 threaded in a lugv 99 ona block 83, and spring |99 tends to turn the magnet on their pivot 91and hold the end of the magnet against the screw 99. It will be' evidentthat by turning the screw 99 the ends oi the magnets may be adjustedtoward and from the elements 99-94 to polarize these elements and varythe magnitude of the iiux therein the same as in the form of Fig. 5. l

In Fig. 7 is shown a gravitationally oriented compensating device inwhich the-polarity may be changed or its eiiect varied. In this iigurethe compensating device is shown with an inductor system correspondingto that of Fig.v 1, the inductor 29 being rotated by the upright shaft23. Mounted by a ball and socket joint I9| and |92 in the lower wall oithe housing 21 is the magnetic element |93 and it is thusgravitationally oriented to swing in all directions andis maintained inthe upright position in all positions of the inductor compass and of thecraft on which it ismounted. Mounted on the lower part of the member|93, which may be of soft iron, permalloy or other suitable magneticmaterial, is a support |94 pivoted to member |93 at |95. The member |94carries two magnets I96-I91 arranged with their poles reversed asindicated. The pivot |95 may be relatively tight to provide sufficientfriction to hold the element |94 in any given position, or frictionmeans may be provided, such as a friction washer. Thus if the compass isused in a location where north polarity is desired for compensating forthe vertical component of the earths magnetic eld in the compass, thenthe element |194 is turned on its pivot to a position indicated in thedotted lines to bring thenorth pole of magnet |96 adjacent to the member|93 and to move the south pole of the magnet |91 away from this element.Thus the element |03 will be polarized by the magnet |96 and thestrength of its iield or flux will depend on the proximity of thismagnet to the element |93. A handle |98 may E be provided on themember'A |94 to shift it to the position desired. It will also beevident that clamping or locking means may be providedrto secure theelement 94 in adjusted position.

In Figs. 15, 16 and 17 my compensating device is shown as applied to asomewhat different inductor compass than that shown in Fig, 1. Thepurpose of this arrangement is to provide a rugged inductor compass inwhich the ilexible shaft here` tofore used to set a course is entirelyeliminated and the desired course is selected by purely elec-- tricalmeans. This improved electrical compass is .based on a system by whichit is possible to setthe desired Vcourse by an electrical bridge systemrather than by the use of a iiexible shaft or other mechanicalarrangement. A typical lay-4 out of this typ'e' of compass is shown inFigs. 15, 16

and 17 wherein a drive-wheel 24 similar to that used in Fig.'l ismounted on the upright shaft |99 Y which drives an inductor amature orcoils I9.

The rotating inductor armature II9 produces au. E. M. F. in its windingsin the well known manner of turning in the earths magnetic eld. Thearmature winding may be any one of several types, but it vis desirablethat efiicient symmetry of the windings be selected so that severalcommutator segments can be used and connected to these windings. Insteadof using two or four brushes pressing on the commutator, in thisparticularV design it has been found more satisfactory to use arelatively large number, for the use ofa greater number permits of amore uniform scale of direction. 'I'he arrangement of the brush andcommutator system is shown more clearly in Figs. 16 and 1'7 whereinsulating blocks |I2 carry the brushes ||3 which make contact with thecommutator comprising the segments III. The electrical layout of thissystem is shown in Fig. 16 where the commutator and brush assembly isindicated in the upper part of the gure. A lead extends from each brushto a point indicated at ||5 on a ring resistance balance circuit II4,the

points of contactto this ring being symmetrical and equal to the numberof brushes employed as shown in Fig. 16. The indicator mechanismindicated at ||1 is shown connected across the ring resistance balancecircuit ||4 by sliding contacts I IS-I |9. The sensitivity of thisindicator mechanism may be`controlled by a shunt in the usual manner asindicated at I I8, Fig. 2.

The Arotation of the inductor armature in the earths magnetic ield givesrise to an E. M. F. which depends on thel relative position of themagnetic eld and the brush system. As the s relative position of theimpressed magnetic eld changes in respect to the fixed brush system, soalso the relative position of high and low potential inthe ringresistance balance circuit II4. Thus a point will always be found wherethe contacts IIB-|19 are at zero potential no matter what the positionof the impressed magnetic eld. Moreover, the position of the contactswhere they are at zero and the `same potential, or when the indicator I1shows zero average current,bears a denite relation to the angularposition of the earths magnetic eld to a, reference axis. Such a devicemay therefore be employed to indicate direction and the contacts may bearranged to slide over a suitable scale with all the points of thecompass markedthereon, and by so lsetting the contacts for a givencourse the pilot may judge when he is on a selected course and when heis off it, and which Way he is oi by simply observing the' indicator|I1. Thus contacts II8 and ||9` 55 may be mounted on a support to turnor slide on the ring I|4 to set the desired course, and whenearthsmagnetic eld and the potential distribution in the ring circuit I I4changes with it and is indicated by the position of zero E. M. F.

' As shown in the other devices this type of compass may be rigidlymounted on the frame 22 of the craft and the deviations introduced bythe vertical component of the earths magnetic field compensated for byany of, the gravitationally oriented compensating devices' previouslydescribed. In Fig. 15v the compensating device shown -is the magnet 46the same as that shown in Fig. 1 The advantage gained by being able touse a lrigidly-m unted inductor system is so great that theinherentlowsensitivity of this type of device'can-be overcome by using largeinductor systems, yet maintaining the total weight at suitable values.It will be clear that 6 Y the compensation of the vertical component ofthe earth's magnetic field may be accomplished either bythe permanentmagnets or by means of an electromagnet which is gravitationallyoriented as well as by the small permanent mag' compensator is shown asmounted above the needle, but it may of course be mounted below it.

In these figures the magnet of the iixed needle type compass indicatedat |20 is swung between two heavy copper or aluminum plates |2| and |22on the pivots |23 to provide electrodynamic damping. It will beevident'tha't movement of the magnet would induce eddy currents in theseplates to produce the damping effect. A circular scale |24 may beattached to the needle and graduated to read from zero to three hundredand sixty degrees. The gravitationally oriented compensator |25 ismounted on the supports |28 on the ball and socket |21 the same asin theother figures, the compensator |25 being either a per-- manent or anelectromagnet and heavier below this support so that it is alwaysmaintained in an upright position.

It will be evident that I have provided an effective means forcompensating for the effects of the vertical component of the earth'smagnetic iield as the ship pitches or rolls out of the 'horizontalplane, and that it maybe applied to all magnetic compasses involvingeither a per--v marient magnet needle or a rotating inductor system, andthat it is much simpler and. more easily mounted and operated than theold system where .the entire system is gravitationally oriented.

4, 'rue preferred embodiment ie'tnezdiscioeed in F188. l, 2a, 'l to 15inclusive, 18 a.!11 19A comprising a magneticmeans gravitationallyoriented independently of the means responsive to the earths magneticfield so that this compensating means can be used with compassesnormally mounted a fixed position on a mobile craft.

The invention described herein may be manufactured andused byo'fforthe-Government of the United States of America for governmental purposeswithout thepayment of any royalties thereon or therefor. v

Having thus set. forth the nature ofvmy invention, what I claim is:

1. In a compass, means responsiveV to the earths magnetic eld toindicate direction and mounted on a mobile craft to turn about an axisarranged in a 'normally fixed position relative to said craft so thatsaid axis tips with the craft and is maintained in the same relativeposition with respect thereto, a device mounted adjacent said responsivemeans capable of creating a magnetic field to cancel o ut the eifect ofthe vertical component ofthe earths magnetic eld, means for mountingsaid device for universal swinging movements, and gravitationallycontrolled means for stabilizing said device in an uphtpositionindependently of movements of the craft.

2. In a compass, an inductor system, means for l rigidly mounting theinductor system on a mobile craft to rotate about an axis which is iixedrelative to the craft and normally substantiallyver- Y tical, acompensating magneticdevice adjacent the inductor, a universal mountingfor said delvice permitting universal rocking movement. and said devicebeing pendulous in sai'd mountingso that it is gravity operated toautomatically main-- tain the device in substantially the verticalposition as the craft tips in various directions to cancel out theeffect of the vertical component of the earths magnetic field only.

3. In a compass, an inductor system, means for rigidly mounting theinductor system on a mobile craft to rotate about a normallysubstantially vertical axis fixed' relative to the craft so that it tipswith the craft, a vertical compensating magnetic device adjacent theinductor, means mounting the compensating device for universal swingingmovements, said device being pendulous in said mounting, and means formounting the compensating device to permit adjustment of the devicetoward and from theinductor to vary the effect of said device on thesystem.

4. In a compass, an inductor system including an inductor mounted torotate about a normally upright axis, means for rigidly mounting thesystem on a mobile craft with said axis fixed relative to the craft, acompensating magnet located in a substantially 4vertical positionadjacent said,

inductor, means for molmting the magnet for universal rocking movementin all directions independently of the inductor and said magnet' beingweighted so that it is automatically main tained in the substantiallyvertical position by gravity.

5. In a compass, means responsive tothe earths magnetic field toindicate direction, aligned elements of magnetic material locatedadjacent said means and forming a gap between adjacent ends. a pair ofpolarizing magnets arranged on opposite sides of said elements and withtheir poles in reversed relationvwith respect to said elements,

and means for shifting the magnets toward and from the elements tobridge said gap to vary the polarization of the elements.

y 8, In a compass, the combination of an inductor system rigidly mountedon a mobile craft and including an inductor element rotating about anaxis normally substantially vertical and fixed relative tothe craft soas to tip with said craft, a magnetic device capable of producing amagnetic iield adjacent the inductor to cancel out the effect of thevertical component of the earth's magnetic field only, means mountingthe magnetic device for imiversal swinging movements, and said devicebeing pendulous in the said mounting for gravitationally stabilizingsaid -demally substantiallyv vertical which axis is v fixed relative tothe craft so as-to tip with said craft, a magnetic device capable ofproducing a magnetic field adjacent said responsive means to cancel theeect of the vertical component of the earths magnetic field only, meansmounting the magnetic device for universal swinging movements, and saiddevice being pendulous in said for gravitationally stabilizing saiddevice independently of the responsive means as the craft tips.

8. In acompass, an inductor system, means for `rigidly mounting theinductor system on a mobile craft. a compensating magnet, means mountingthemagnet for universal swinging movements with nevend adjacent saidsystem and the other end remote therefrom,'said magnet being pendulousin said mounting, and said end of the magnet being asymmetrical so itAhas an end oblong in cross section toproduce a stronee magnetic held inone plane than in others at an angle thereto to compensate for theasymmetrical magnetism of the craft.

9. In a compass, an inductor system, means for rigidly mounting theinductor system on a mobile craft, a compensating magnet, means mountingthe magnet for universal swinxing movements with one end adjacent saidsystem and the other end remote therefrom, said magnet being pendulousin said mounting, and said end of the malnet being asymmetrical so ithas an oblong end to `produce asstronger magnetic field in one planethan in others at an angle thereto to compensate for the asymmetricalmagnetism of the craft.

ROSS GUNN.

